1. Field of the Invention
This invention relates to a control system for an AC motor and more particularly to a control system variably controlling a DC link voltage of an inverter driving the AC motor with the use of a converter.
2. Description of the Background Art
In order to control an AC motor with the use of a DC power supply, a control system including an inverter has generally been employed. For example, as described also in Japanese Patent Laying-Open No. 2006-311768 (hereinafter referred to as “PTD 1”), a configuration variably controlling a DC link voltage of an inverter with the use of a boost converter has been known. Thus, as an output voltage from a boost converter (that is, a DC link voltage of an inverter) is boosted from an output voltage from a DC power supply (representatively, a battery), the AC motor can advantageously be driven at higher torque and higher rotation.
PTD 1 above describes variable control of a voltage on a DC link side of an inverter, that is, an output voltage from a boost converter, so as to maintain a modulation factor in a specific control scheme at a target value during control of an AC motor in which pulse width modulation (PWM) control and rectangular wave voltage control are selectively applied. By doing so, loss in the overall system can be lowered by maintaining the modulation factor (degree of modulation) at the target value.